just train
Instead of using the word challenging you can use the word gifted, special, special gifted.
or
Will, when, why, it, can
It only looks like a letter X. In fact it is a cross.
Myself
I have a stomach ache.
mixture
are
There are different adjectives and verbs that can be used instead of the word criss cross. You might use the word intersect, overlap and also network. This would mostly apply to lines or roads. But you can also use the connotation move back and forth through and over which is basically the same thing.
used to be
is, it, in the past.
no "It" is not used instead of he and she...